president obama said those responsible will feel the full weight of justice. >> we will find out who did this and why p they did this. any responsible individuals, any responsible groups will feel the full weight of justice. >> reporter: this evening in boston authorities offered few new details. >> the fbi is taking the lead in this invest sgags. it's criminal that is a potential terrorist investigation. comfortable racing weather for the runners ready to compete for personal glory or just the honor of it all. it's usually a joyous day off. today someone stole all of that killing and maiming innocence who can never forget the day they ran when the finish line was strong with crime scene tape. >> mat has made his way up to boston. good evening. >> reporter: those patients are in extremely good hands. this is a well regarded hospital. it's the oldest one level one trauma. i'm joined by three eyewitnesss to this tragedy. i'm happy to say they were not among the injured. thank you for joining us. i know you were making your way around the finish line. how close did you get before the bo